I. Field of the Invention
This invention embodies compositions and methods related to immunology and medicine. In particular the invention is related to diagnostics and therapeutics for the diagnosis and treatment of autoimmune conditions, particularly diabetes.
II. Background
Antigen vaccination can be used for the induction of T-cell tolerance in autoimmunity. Administration of autoantigenic proteins or peptides in solution can blunt the initiation and/or progression of autoimmunity in experimental models of autoimmune disease (Wraith et al., 1989; Metzler and Wraith, 1993; Liu and Wraith, 1995; Anderton and Wraith, 1998; Karin et al., 1994). However, limited clinical trials in humans employing similar strategies have almost invariably met with failure (Weiner, 1993; Trentham et al., 1993; McKown et al., 1999; Pozzilli et al., 2000; Group, D.P.T.-T.D.S. 2002; Kappos et al., 2000; Bielekova et al., 2000). This suggests that the principles guiding the choice and conditions of treatment are poorly defined and, as a result, inadequate for human application.
Spontaneous organ-specific autoimmune disorders result from complex responses against numerous epitopes in multiple antigens that arise spontaneously in a stochastic and often unpredictable sequence. This complexity is compounded by the fact that lymphocyte clones recognizing identical epitopes engage antigen/major histocompatibility complex (MHC) molecules within a broad range of avidities, the strength of which correlates with pathogenic potential (Amrani et al., 2000; Santamaria, 2001; Liblau et al., 2002). Consequently, the outcome of any immunization strategy for the prevention of autoimmunity is likely to be influenced by the choice of autoantigen(s), dose, periodicity of treatment, and route and form of administration.
Type 1 Diabetes (T1D) in mice is associated with autoreactive CD8+ T-cells. Nonobese diabetic (NOD) mice develop a form of T1D, closely resembling human T1D, that results from selective destruction of pancreatic β cells by T-cells recognizing a growing list of autoantigens (Lieberman and DiLorenzo, 2003). Although initiation of T1D clearly requires the contribution of CD4+ cells, there is compelling evidence that T1D is CD8+ T-cell-dependent (Santamaria, 2001; Liblau et al., 2002). It has been discovered that a significant fraction of islet-associated CD8+ cells in NOD mice use CDR3-invariant Vα17-Jα42+ TCRs, referred to as ‘8.3-TCR-like’ (Santamaria et al., 1995; Verdaguer et al., 1996; Verdaguer et al., 1997; DiLorenzo et al., 1998). These cells, which recognize the mimotope NRP-A7 (defined using combinatorial peptide libraries) in the context of the MHC molecule Kd (Anderson et al., 1999), are already a significant component of the earliest NOD islet CD8+ infiltrates (DiLorenzo et al., 1998; Anderson et al., 1999; Amrani et al., 2001), are diabetogenic (Verdaguer et al., 1996; Verdaguer et al., 1997), and target a peptide from islet-specific glucose-6-phosphatase catalytic subunit-related protein (IGRP) (Lieberman et al., 2003), a protein of unknown function (Arden et al., 1999; Martin et al., 2001). The CD8+ cells that recognize this peptide (IGRP206-214, similar to NRP-A7) are unusually frequent in the circulation (> 1/200 CD8+ cells) (Lieberman et al., 2003; Trudeau et al., 2003). Notably, progression of insulitis to diabetes in NOD mice is invariably accompanied by cyclic expansion of the circulating IGRP206-214-reactive CD8+ pool (Trudeau et al., 2003), and by avidity maturation of its islet-associated counterpart (Amrani et al., 2000). More recently, it has been shown that islet-associated CD8+ cells in NOD mice recognize multiple IGRP epitopes, indicating that IGRP is a dominant autoantigen for CD8+ cells, at least in murine T1D (Han et al., 2005). NOD islet-associated CD8+ cells, particularly those found early on in the disease process also recognize an insulin epitope (Ins B15-23 (Wong et al., 1999)).
Association studies have suggested that certain HLA class I alleles (i.e., HLA-A*0201) afford susceptibility to human T1D (Fennessy et al., 1994; Honeyman et al., 1995; Tait et al., 1995; Nejentsev et al., 1997; Nakanishi et al., 1999; Robles et al., 2002). Pathology studies have shown that the insulitis lesions of newly diagnosed patients consist mostly of (HLA class I-restricted) CD8+ T-cells (Bottazzo et al., 1985; Atkinson and Maclaren, 1990; Castano and Eisenbarth, 1990; Hanninen et al., 1992; Itoh et al., 1993; Somoza et al., 1994; Atkinson and Maclaren, 1994; Moriwaki et al., 1999; Imagawa et al., 2001), which are also the predominant cell population in patients treated by transplantation with pancreas isografts (from identical twins) or allografts (from related donors) (Sibley et al., 1985; Santamaria et al., 1992).
Insulin is a key target of the antibody and CD4+ response in both human and murine T1D (Wong et al., 1999; Palmer et al., 1983; Chentoufi and Polychronakos, 2002; Toma et al., 2005; Nakayama et al., 2005; Kent et al., 2005). The human insulin B chain epitope hInsB10-18 is presented by HLA-A*0201 to autoreactive CD8+ cells both in islet transplant recipients (Pinkse et al., 2005) and in the course of spontaneous disease (Toma et al., 2005). In addition, four additional peptides have been identified from mouse pre-proinsulin 1 or 2 that are recognized by islet-associated CD8+ T-cells from HLA-A*0201-transgenic mice in the context of HLA-A*0201.
IGRP, which is encoded by a gene (located on chromosome 2q28-32 (Martin et al., 2001)) that overlaps a T1D susceptibility locus, IDDM7 (2q31) (Pociot and McDermott, 2002; Owerbach, 2000), has also been recently identified as a beta-cell autoantigen of potential relevance in human T1D (Takaki et al., 2006). Two HLA-A*0201-binding epitopes of human IGRP (hIGRP228-236 and hIGRP265-273) are recognized by islet-associated CD8+ cells from murine MHC class I-deficient NOD mice expressing an HLA-A*0201 transgene (Takaki et al., 2006). Notably, the islet-associated CD8+ T-cells of these ‘humanized’ HLA-A*0201-transgenic mice were cytotoxic to HLA-A*0201-positive human islets (Takaki et al., 2006).
T1D in NOD mice can be prevented by expansion of low avidity autoreactive CD8+ T-cells. Administration of soluble peptides (without adjuvant) is an effective way of inducing antigen-specific T-cell tolerance (Aichele et al., 1994; Toes et al., 1996). Previously, it was shown that treatment of pre-diabetic NOD mice with soluble NRP-A7 blunted avidity maturation of the IGRP206-214-reactive CD8+ subset by selectively deleting clonotypes expressing TCRs with the highest affinity for peptide/MHC (Amrani et al., 2000). These observations raised the possibility that NRP-A7's anti-T1D activity was mediated also by fostering occupation of the ‘high avidity clonotype niche’ (emptied by NRP-A7 treatment) by ‘low avidity’ (and potentially anti-diabetogenic) clones. To test this hypothesis, altered peptide ligands (APLs) were identified with partial, full or super agonistic activity for IGRP206-214-reactive CD8+ T-cells and compared their anti-T1D activity over a wide dose-range.
Chronic treatment with moderate doses of an intermediate affinity APL (NRP-A7) or high doses of a low affinity APL (NRP-I4) afforded T1D protection. This was associated with local accumulation of low avidity IGRP206-214-reactive CD8+ cells at the expense of their high avidity counterparts, which were deleted. Unexpectedly, chronic treatment with high doses of a high affinity APL (NRP-V7) or the natural ligand (IGRP206-214) only afforded marginal protection. Strikingly, the islets of these mice contained almost no IGRP206-214-reactive CD8+ cells, but increased populations of CD8+ cells recognizing other IGRP epitopes. This led us to conclude that peptide therapy in autoimmunity may be most effective when it fosters occupation of the target organ lymphocyte niche by non-pathogenic, low avidity clones (Han et al., 2005), a prediction supported by mathematical modeling (Maree et al., 2006). Unfortunately, this outcome occurred only within a narrow range of APL dose and avidity (for target TCRs), suggesting that peptide therapy is ill-suited to prevent or cure T1D.
Thus, there remains a need for additional compositions and related methods for the treatment of diabetes, as well as other autoimmune disorders.